Try to fix linux compilations problems (apparently on some systems

Screen is defined, which then interferes with out Screen class).

src/guiengine/screen.hpp

@@ -94,7 +94,7 @@ namespace GUIEngine
      *
      * \ingroup guiengine
      */
-    class Screen : public AbstractTopLevelContainer
+    class GUIEngine::Screen : public AbstractTopLevelContainer
     {
     private:
         /** True if the race (if it is running) should be paused when this

src/states_screens/dialogs/track_info_dialog.cpp

@@ -173,7 +173,7 @@ TrackInfoDialog::~TrackInfoDialog()
 {
     // Place focus back on selected track, in case the dialog was cancelled and we're back to
     // the track selection screen after
-    Screen* curr_screen = GUIEngine::getCurrentScreen();
+    GUIEngine::Screen* curr_screen = GUIEngine::getCurrentScreen();
     if (curr_screen->getName() == "tracks.stkgui")
     {
         ((TracksScreen*)curr_screen)->setFocusOnTrack(m_ribbon_item);